212 INVERTEBRATE ZOOLOGY 
Fertilization: the union of the spermatozoén and the ovum. 
Flagellum: a vibratory thread-like projection of certain cells; hydroids, 
162, 166; sponges, 183; also of flagellate infusorians, 192. 
Flame cell: the terminal cell of an excretory tubule of flatworms, 78. 
Flexor muscle: a muscle that bends an organ, 37. 
Food vacuole: a globule of water containing food particles; Paramecium, 
186; Vorticella, 189; Amoeba, 195. 
Front: the anterior median portion of the epicranium, 12. 
Funiculus: a mesenteric strand connecting the stomach pouch with the 
body-wall in bryozoans, 86. 
Funnel: the siphon of a cephalopod, 124. 
Ganglion: an aggregation of nerve cells; grasshopper, 18; crayfish or 
lobster, 41; crab, 44; Daphnia, 57; Nereis, 66; earthworm, 74; mussel, 
97; clam, 111; snail, 121; squid, 183; Molgula, 138. 
Gastrolith : a calcareous body sometimes present in the stomach of crusta- 
ceans, 40. 
.Gastro-vascular space: the central cavity in Cnidaria; Hydra, 160; tubu- 
larian, 164; campanularian, 170; Gonionemus, 176; sea anemone, 179. 
Gastrula: a stage in the development of the embryo in which two cell 
layers only are present, the ectoderm and the entoderm. 
Gena: the lateral portion of the epicranium in insects, 12. 
Genital plate: a sclerite at the posterior end of the abdomen in the male 
grasshopper, 11. 
Giant fibers: three large fibers in the dorsal portion of the nerve cord in 
the earthworm, 75. 
Gill: an organ for the breathing of air contained in the water; crayfish or 
lobster, 35; crab, 43 ; sow-bug, 47; amphipod, 49; Caprella, 50; Nereis, 
63; mussel, 90; oyster, 100; clam, 104; squid, 127. 
Gill-filament : ciliated vertical ridges on the surface of the gills of lamelli- 
branchs; mussel, 94; clam, 108. 
Gizzard: a portion of the alimentary tract with thickened muscular 
walls, 71. 
Glochidium : the larval form of Anodonta and Unio, which lives a parasitic 
life in the skin of fishes, 97. 
Gonotheca: the cuticular outer covering of the blastostyle, 170. 
Green gland: the kidney of a malacostracan crustacean, 30. 
Hemal: pertaining to the blood system. 
Head: the anterior body-division of the higher animals. 
